It is the general practice in the installation of electrical transmission towers to provide electrical ground connections, known as "ground rods." The customary installation includes the driving of ground rods contiguous to the towers to a depth of as many feet as practical. These rods are frequently copper-clad, have threaded ends, and are connected one to the other by threaded couplings. At the exterior or exposed end of the rod, it is customary to connect a copper line to the tower and clamp it to the rod by a clamp, held normally in place by a set screw.